Форуми / Cotonti / Extensions / Support / CKeditor - How can we change the output?

There is another way that meet you needs. It's improvement of default Image dialog for adding Rel attribute.

Here is the sample code for (ckeditor/lib/plugins/image/dialogs/image.js):

{
    type : 'text',
    id : 'txtdlgGenRel',
    label : editor.lang.link.rel,
    'default' : '',
    validate : function() {
	var regexValidRel = /^\w+$|^$/i;
	var aMatch = this.getValue().match(regexValidRel), isValid = !!(aMatch);
	if (!isValid)
	    alert('Not allowed type of Rel');
	return isValid;
    },
    setup : function(type, element) {
	if (type == IMAGE) {
	    var genRel = element.getAttribute('rel');
	    if (!genRel && element.$.prop('rel'))
		genRel = element.$.prop('rel');
	    this.setValue(genRel);
	    var regexValidRel = /^\w+$|^$/i;
	    var rel = element.$.prop('rel');
	    aMatchRel = (rel ? rel : '').match(regexValidRel);

	    this.attributesInStyle = {
		rel : !!aMatchRel
	    };
	}
    },
    commit : function(type, element) {
	if (type == IMAGE && (this.getValue() || this.isChanged())) {
	    element.setAttribute('rel', this.getValue());
	}
    }
}

Full code is here: http://www.cotonti.com/pastebin/170